therefore, screening for anemia during pregnancy is recommended regardless of symptoms.
Table 11.1 Changes in laboratory values in pregnancy
Source: Based on ACOG Practice Bulletin No. 107, 2009.
| Nonpregnant women | Pregnant women | |
|---|---|---|
| Hemoglobin (g/dL) | 12–16 | 11–14 |
| Hematocrit | 36–46% | 33–44% |
| RBC count (× 106/mL) | 4.8 | 4.0 |
| MCV (fL) | 80–100 | = |
| MCHC | 31–36% | = |
| Reticulocytes (× 109/L) | 50–150 | = |
| Ferritin (ng/mL) | >25 | >20 |
| RDW (red cell distribution width) | 11–15% | = |
=, unchanged.
Diagnostic work‐up and treatment
Causes of anemia may be classified by pathophysiology, such as comparing acquired versus inherited causes, or mechanisms of anemia such as decreased RBC production versus increased destruction. In clinical practice, more often the evaluation of maternal anemia starts with the mean corpuscular volume (MCV), based on which anemias are defined as microcytic (less than 80 fL), normocytic (80–100 fL) or macrocytic (greater than 100 fL) (Figure 11.1).
Macrocytic anemia
Figure 11.1 shows the appropriate work‐up for the search of causes in the presence of macrocytic anemia. Vitamin B12 deficiency is rare, as most healthy individuals have 2–3 years’ storage available in the liver. However, vitamin B12 deficiency can be encountered in individuals who have undergone bariatric surgery with partial gastric resection and are noncompliant with recommended vitamin B12 supplementation (350 μg/day sublingually plus 1000 μg IM every three months if needed), in individuals with pernicious anemia (an extremely uncommon autoimmune disease in women of reproductive age which is diagnosed by the presence of serum intrinsic factor antibodies), and in those with malabsorption (e.g., Crohn disease or ileal resection). Folate deficiency is less common today given the supplementation of foods with folate and universal folic acid supplementation in pregnancy. Recommended folate requirements are 400 μg/day during pregnancy, with higher doses recommended in the presence of multiple gestations, hemolytic disorders such as sickle cell anemia or thalassemia, and in patients taking antiepileptic drugs (AED) or sulfa drugs (e.g., sulfasalazine). In addition to macrocytic anemia, folate deficiency may also cause thrombocytopenia.
Figure 11.1 Causes of maternal anemia, classified by mean corpuscular volume (MCV).
If a diagnosis of folate deficiency is made, or the woman had a prior pregnancy affected by a neural tube defect, the recommended dose of folic acid is 4 mg/day. Anemia due to folate or B12 deficiency should respond briskly, with an elevated reticulocyte count, within 4–7 days of beginning treatment. In the case of macrocytic anemia with normal folate and vitamin B12 levels, a consultation with a hematologist is indicated for bone marrow biopsy.
Normocytic anemia
The recommended laboratory evaluation for normocytic anemia is displayed in Figure 11.2. A high reticulocyte count indicates either hemolysis or blood loss with resultant bone marrow activation. If a normocytic anemia with an elevated reticulocyte count is found, a careful history and evaluation of laboratory studies for hemolysis, such as Coombs test, peripheral smear, and lactate dehydrogenase level, should be undertaken. A normal or low reticulocyte count in the setting of anemia raises concern for iron deficiency (a ferritin level less than 10–15 μg/dL is diagnostic) or bone marrow suppression/disorders. Low reticulocyte count with normal or high serum ferritin levels can be seen in the presence of hypothyroidism or chronic disorders, such as inflammatory bowel disease, systemic lupus erythematosus, granulomatous infections, malignant neoplasms, and rheumatoid arthritis. Hematology consultation for further assessment is indicated in these circumstances.
Figure 11.2 Algorithm for evaluation of normocytic anemia.
Mixed nutritional deficiencies (folate and iron) may lead to normocytic anemia in pregnancy, but routine supplementation makes the probability of such a scenario low. If concern for a mixed nutritional deficiency does arise, the red cell distribution width (RDW), a marker of increased variability in red cell size or anisocytosis, is a useful indicator as an RDW greater than 15% indicates the presence of nutritional deficiencies.
Microcytic anemia
Most cases of microcytic anemia in pregnancy are due to iron deficiency anemia. Evaluation of a ferritin level should be the next step, as shown in Figure 11.3. Serum ferritin is the most sensitive and specific screening test for iron deficiency, with a level less than 10–15 μg/dL indicating depleted iron stores. If serum ferritin is normal or high, the next step is hemoglobin electrophoresis to evaluate for a thalassemia. Such situations usually warrant consultation with a hematologist for further evaluation and bone marrow biopsy as indicated.
Figure 11.3 Algorithm for evaluation of microcytic anemia.
Iron supplementation in pregnancy
In a typical singleton gestation, maternal iron requirements (including blood volume expansion as well as fetal and placental requirements) average 1 g for the entire pregnancy, with this requirement further increased in the setting of multiple gestations. In a landmark study of healthy, nonanemic, menstruating young women who
